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Corrosion Under Insulation (CUI) is a severe form of localized corrosion caused by some insulating products - namely coated or molded-on insulation.
The largest contributing factor to CUI is the presence of water or another electrolyte that leaves salts on the metal surface of actuators, valves, pipe, cable trays, and electrical wire troughs. Coated fire protection is applied with an epoxy that when exposed to cycles of heating an cooling has the same disastrous effect of other electrolytes.
A study performed by Exxon Mobil Chemical found that Corrosion Under Insulation causes the highest incidence of leaks in the refining and chemical industries - more even than process corrosion.
40 - 60% of piping maintenance costs are related to CUI. *Reference: Insulation.org
Inspecting for CUI
Inspecting for corrosion under coated or molded-on insulation requires cutting plugs in the insulation, removing the section of insulation, and performing ultrasonic testing. While this is the most common method, it generally leads to more moisture entering the space between insulation and equipment - causing further corrosion-related damage. It is also important to note that CUI is most often a localized issue and will only be discovered if insulation is removed at the exact right location.
Inspecting for corrosion under blanket or jacket insulation requires only that you remove the insulation blanket.
Preventing CUI
CUI prevention starts with removal of the insulation systems known to plague equipment. In some cases protective coatings meant for atmospheric surfaces are applied to deter the effects of CUI but in most cases these coatings do nothing but promote corrosion. The best prevention is careful selection of insulation materials - Products like UniTherm’s FirePro system provide a reliable source of fire protection without the risks of corrosion under insulation. |
